The instructions are in the repo: https://github.com/microsoft/AirSim/blob/4d07f6e9bf21fd4418da8a2b5e8de6c55ede8ff8/docs/airsim_ros_pkgs.md

i followed that tutorial.When i tried to do catkin build, i am getting the following error [build] Error: Unable to find source space /home/aimotion/src

Ok but your question then should be on the error and what have you tried so far

when I do catkin build,the following error;

Errors     << airsim_ros_pkgs:cmake /home/aimotion/catkin_ws/src/ros/logs/airsim_ros_pkgs/build.cmake.001.log
CMake Error at CMakeLists.txt:7 (add_subdirectory):
  add_subdirectory given source
  "/home/aimotion/catkin_ws/src/ros/src/airsim_ros_pkgs/../../..//cmake/rpclib_wrapper"
  which is not an existing directory.


CMake Error at CMakeLists.txt:8 (add_subdirectory):
  add_subdirectory given source
  "/home/aimotion/catkin_ws/src/ros/src/airsim_ros_pkgs/../../..//cmake/AirLib"
  which is not an existing directory.


CMake Error at CMakeLists.txt:9 (add_subdirectory):
  add_subdirectory given source
  "/home/aimotion/catkin_ws/src/ros/src/airsim_ros_pkgs/../../..//cmake/MavLinkCom"
  which is not an existing directory.

Please format the error using 101010 button. I believe there is a workaround as you are missing airsim_node when compiling.

install(TARGETS
    #list of nodes
    airsim_node
    pd_position_controller_simple_node
    DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
)

Refer to: https://github.com/microsoft/AirSim/pull/2706/commits/4b8dd4069d76c6c485cf8dafff0df373d59867ed This is not a ROS issue but an issue with Airsim, I suggest you raise issues in the repo.